This invention relates to an endoscope
Endoscopes (also referred to as endoscopic optical systems) of the type to which the invention relates generally have a proximal main body, distally connected to which there is a tubular shaft region. In such devices, e.g. ureterscopes, the shaft region is of rigid construction and has a relatively small diameter in comparison to its length. Fibrous light guides can be positioned in the tubular shaft region, also termed cover tube or optical tube, which extend from a proximal entry point in the vicinity of the main body to the distal end of the optical tube, and serve to illuminate the field to be observed. Furthermore, the optical tube accommodates the actual devices for transmitting the image, optionally in a further tube (system tube).
The image transmission occurs between a lens provided in the distal end region of the system tube and a proximal device for image viewing, e.g., an eyepiece or a video camera, etc.
Particularly in endoscopes with a small diameter, a so-called fiber optic image guide is used for transmission. The image guide extends between the distal lens and the proximal image viewing devices. Such a fiber optic image guide comprises a plurality of longitudinally extending fibers of transparent material, particularly of materials based on glass, e.g., quartz glass.
A substantial problem with conventional endoscopes in this connection is that the used image guides of, e.g., quartz glass have different expansion characteristics from the surrounding regions of the endoscope, e.g., the system tube, which comprises metal.
In particular, a rigid endoscope of small diameter, e.g., a ureterscope, must be able to withstand bending of its shaft region during use. The image guide is generally not centrally disposed so that bending of the endoscope results in stretching or buckling which can be accommodated by the metallic system tube without great problems but can be accommodated only to a limited extent by a fixed xe2x80x9cglass fiberxe2x80x9d image guide positioned therein. Similar problems occur when heat sterilizing endoscopes with fiber optic image guides. The image guide and endoscope expand to different extents and at different speeds from each other and stresses can thus occur, particularly if both ends of the image guide are fixed.
There are various possibilities for dealing with the above problems. In this connection, e.g., WO 9605764 discloses an endoscope of the type referred to above in which the image guide is fastened in the system tube only at its distal end. The proximal end, on the other hand, is movably received in the main body. A disadvantage with this known construction is that, particularly having regard to the very short focal lengths of the optical components which are used, a correction must be effected each time the proximal end of the image guide moves, which necessitates a relatively large construction expense.
It is thus an object of the invention, starting from the prior art, to provide an endoscope in which the occurrence of stresses between the image guide and endoscope can be prevented at low constructional expense.
In the endoscope in accordance with the invention it is provided that the image guide is fixedly secured in the endoscope substantially only at its proximal end region while the remaining image guide region to its distal end is mounted to be freely movable in the axial direction.
In conventional devices, which have a main body and a shaft attached thereto, the fastening of the image guide is effected, e.g., in the region of the main body while its region situated within the shaft is not fixed. Potential thermal influences or bending, which result in differential elongation of the image guide and the surrounding endoscope, can thus be compensated for without difficulty, the distal end of the image guide moving in the axial direction with respect to the endoscope. In order to make constant optical imaging quality possible, the invention further provides that the objective is also mounted movably with respect to the endoscope and is so connected to the distal end of the image guide that common movement occurs with a constant spacing.
The term xe2x80x9cobjectivexe2x80x9d means any and all optical devices which make imaging of the field of view at the distal end of the image guide possible. It can be a lens or lens system, wherein the connection between the image guide and objective can be effected, e.g., by adhesive. Other types of connection are, however, also possible.
The invention is preferably implemented in a rigid endoscope of small diameter, i.e., an endoscope which has a main body, from which a rigid, relatively long shaft region of small diameter extends. Such an endoscope can be bent within limits during use, whereby the relative movement described above between the image guide and endoscope occurs which is compensated for in a particularly simple manner in devices in accordance with the invention.
The proximal end of the image guide is generally fixedly mounted in the main body of the endoscope. For this purpose, an appropriate fastening device, for instance, can be provided in the main body which holds the proximal end of the image guide at a constant distance from the image viewing devices. The remaining region of the image guide is held freely axially movable up to its distal end, the distally provided objective being axially movably mounted with respect to the endoscope and connected to the distal end of the image guide.
It would be possible, e.g., for the objective to be a single, e.g., gradient lens which is secured by adhesive to the distal end of the image guide. A further advantageous embodiment of the invention provides that the objective is accommodated in an objective tube which is mounted to be axially movable with respect to the endoscope or the surrounding system tube. The distal end of the image guide is connected by adhesive or the like to the proximal end of the objective tube or to the proximal lens of the objective. This embodiment may be realized in a particularly simple manner, particularly if the objective comprises a number of lenses, and allows simultaneous tolerance-free movement of the light guide and objective.
It can be provided in a further advantageous embodiment that the objective tube or the objective is received in the endoscope secured against rotation. This can be achieved, e.g., by providing an elongated projection on the objective tube which engages in a suitable groove in the system tube.
The advantages of the invention reside substantially in the particularly simple constructional implementation with which an optimum optical imaging quality is always ensured, even under widely varying operational conditions. Due to the fact that the distal objective is axially movably accommodated in the endoscope and is automatically appropriately moved axially in the event of potential, e.g., thermally induced, changes in length of the image guide while maintaining the optical conditions, particularly simple adjustment is possible.